Detection and Chiral Recognition of α-Hydroxyl Acid through 1 H and CEST NMR Spectroscopy Using a Ytterbium Macrocyclic Complex.

Chiral α-hydroxyl acids are of great importance in chemical synthesis. Current methods for recognizing their chirality by 1 H NMR are limited by their small chemical shift differences and intrinsic solubility problem in organic solvents. Herein, we developed three YbDO3A(ala)3 derivatives to recognize four different commercially available chiral α-hydroxyl acids in aqueous solution through 1 H NMR and chemical exchange saturation transfer (CEST) spectroscopy. The shift difference between chiral α-hydroxyl acid observed by proton and CEST NMR ranged from 15-40 and 20-40 ppm, respectively. Our work demonstrates for first time, that even one chiral center on the side-arm chain of cyclen could set the stage for rotation of the other two non-chiral side chains into a preferred position. This is ascribed to the lower energy state of the structure. The results show that chiral YbDO3A-like complexes can be used to discriminate chiral α-hydroxyl acids with a distinct signal difference.